1. Field of the Invention
The present invention relates to the production of mechanical and chemimechanical pulp. In particular, the present invention provides a novel method and apparatus for producing pulp from lignocellulosic raw material, such as wood or annual or perennial plants, by mechanical defibration.
2. Description of Related Art
The need to develop mechanical pulping processes is more eminent than ever. The fact of rising electricity prices, which continuously reduce the competitiveness of the processes, is now imminent. Also, the demand for more pulp for even more productive paper machines calls for higher pulp production on existing lines, and this may particularly concern groundwood pulping, because new production lines can be uneconomical to fit into existing facilities.
The grinding of fresh wood is a mature process for the production of pulp for the papermaking process. During the long period of its industrial use the process has many times been the subject of research. The fundamental defibration mechanisms of grinding are complex and difficult to observe, making the process a challenge for researchers for decades. One of the most active periods started in the 1950s when researchers worked with pulp characterization and started to describe the fundamental mechanisms behind defibration. By the early 1990s, however, the situation had stagnated to the point where the well-known operating curves were broadly accepted as physical relations that could not be changed.
There is a need for an improvement of today's wood grinding process.
Various defibration mechanisms have been proposed by Atack and co-workers (1, 2) as well as by Klemm (3), Steenberg and Nordstrand (4).